Recently, human infection of avian influenza (bird flu) has been reported, and heavy damage by human pandemic of bird flu is worried about. So, pre-pandemic vaccine that has a high possibility of being effective against bird flu is being stockpiled worldwide. Also, to administer pre-pandemic vaccine to many people, a study is being carried out on expanding the production quantity of vaccine.
Skin is composed of three parts, an epidermis, a dermis, and a portion of subcutaneous tissue. The epidermis is a layer of about 50-200 μm from the skin surface, and the dermis is a layer of about 1.5-3.5 mm continuing from the epidermis. Because influenza vaccine is generally subcutaneously or intramuscularly administered, it is administered to a lower layer part of skin or a portion deeper than that.
On the other hand, it has been reported that by administering influenza vaccine to an upper layer part of skin as a target site where many immunocompetent cells are present, even if the dosage is reduced, the same immunity acquisition ability as in subcutaneous administration or intramuscular administration can be obtained (Non-patent Document 1). Thus, by administering pre-pandemic vaccine to the skin upper layer part, the dosage can be reduced, so that there is a possibility that bird flu vaccine can be administered to more people. Note that the skin upper layer part refers to the epidermis and dermis of skin.
As the method of administering a drug to the skin upper layer part, methods using a single-needle, a multi-needle, a patch, gas, etc. have been reported. And, if stability and reliability of administration and production cost are considered, as the method of administering a drug to the skin upper layer part, the method using a single needle is most suitable. As the method of administering vaccine to the skin upper layer part using a single needle, a Mantoux method has been known from a long time ago. The Mantoux method is a method that a needle of generally 26-27 G in size having a short bevel needle tip is inserted into skin about 2-5 mm, from an oblique direction of about 10-15° relative to the skin, to administer a drug of about 100 μL.
However, the Mantoux method is difficult in manipulation and is affected by the skill of the doctor giving an injection. In particular, a child has a possibility of moving at the time of administration, so that it is difficult to administer flu vaccine with the Mantoux method. Accordingly, it is desired that a device is developed that can administer vaccine to the skin upper layer part in a simple and convenient manner.
Patent Document 1 describes an injection device for the skin upper layer part in which a limiter having a skin contacting surface is connected with a needle tube. The limiter described in Patent Document 1 is provided around a needle tube about 1-15 mm in diameter, and has a gap with the needle tube. By regulating the length (protruding length) of the needle tube protruding from the surface of the limiter contacting the skin to 0.5-3.0 mm, the drug is administered in the skin.
Also, Patent Document 2 includes description on an injection needle sticking adjustment device that prevents sticking deeper than a target depth. The injection needle sticking adjustment device disclosed in Patent Document 2 includes the one that closely contacts the circumference of a needle tube.
Patent Document 1: Japanese Laid-open Patent Application Publication No. 2001-137343
Patent Document 2: Japanese Laid-open Patent Application Publication No. 2000-037456
Non-patent Document 1: R. T. Kenney et al. New England Journal of Medicine, 351, 2295-2301 (2004)